This invention relates to a radio communication device for use with a mobile communication equipment for carrying out mobile communication such as a portable telephone and a transmission power control method in the radio communication device.
A mobile communication equipment such as a portable telephone generally used is equipped with a function of controlling its own transmission power in response to the distance between a base station and the mobile station when information is transmitted. In a communication system of multiple access type for multiplexing communication channels, transmission power control for fixing power of signals arriving at the base station is absolutely necessary to reduce interference between the communication channels and improve frequency use efficiency.
Particularly with mobile communication equipment adopting a CDMA (code division multiple access) system using spread spectrum modulation techniques, a number of users share a single frequency band, thus the possibility is high that a so-called masking problem in which a signal having large power masks a power having small power will occur, and a problem occurs in which a signal of any other station degrades the line quality of the home station as an interference wave. To solve this problem, hitherto, various transmission power control techniques have been studied; particularly, a transmission power control system with a closed loop is known as a transmission power control system for responding to an interference signal changing instantaneously.
In the CDMA system, highly linear transmission power control in a wide range (for example, 70 to 80 dB) is required. Further, in a wide-band CDMA (W-CDMA) system being developed at present as a next-generation mobile communication system, accuracy requirement of transmission power at the large power time is high and transmission power control of higher accuracy is required.
FIG. 7 is a flowchart to show an example of a transmission power control method in a related art with a closed loop. For a base station and a mobile station to communicate with each other, the mobile station determines a transmission power control bit based on the reception power of a reception wave (desired wave) from the base station at step S101, inserts the transmission power control bit into a transmission signal, and transmits the resultant signal to the base station. The base station receives the signal transmitted from the mobile station, extracts the transmission power control bit from the reception signal at step S105, and controls a variable power amplifier in the base station as indicated in the transmission power control bit at step S106.
Likewise, the base station determines a transmission power control bit based on reception power of the reception wave from the mobile station at step S104, inserts the transmission power control bit into a transmission signal, and transmits the resultant signal to the mobile station. The mobile station receives the signal transmitted from the base station, extracts the transmission power control bit from the reception signal at step S102, and controls a variable power amplifier in the mobile station as indicated in the transmission power control bit at step S103.
Such transmission power control is performed, thereby making it possible to hold reception power almost constant at the base and mobile stations regardless of where the mobile station is located.
To perform transmission power control of high accuracy by the transmission power control method in the related art as described above, variable power amplifiers of high accuracy are required and need to be controlled with high accuracy. However, if an attempt is made to provide variable power amplifier control of high accuracy using variable power amplifiers of high accuracy, the circuit scale becomes large, the power consumption amount increases, and the system or the unit with the variable power amplifier becomes expensive. It may be difficult to cover a wide range of gain control while high accuracy is maintained with one variable power amplifier. Therefore, considering power consumption, portability, system (device) costs, etc., various difficulties are involved in providing transmission power control of high accuracy by the transmission power control method in the related art.
It is therefore an object of the invention to provide a radio communication device that can provide transmission power control means for less consuming power in a simple configuration for improving accuracy of transmission power control and can be miniaturized with lower power consumption and a transmission power control method in the radio communication device.
To the end, according to the invention, there is provided a radio communication device having a transmission power control function of controlling power transmitted to a station to communicate with, the radio communication device comprising variable power amplification means including at least first and second variable power amplifiers, each capable of varying its amplification gain, variable power amplification control means for controlling the variable power amplification means, transmission power detection means for detecting transmission power of the radio communication device based on output of the variable power amplification means, and switch control means for performing switch control for the operation of the variable power amplification means in response to the detected transmission power.
Further, the transmission power detection means detects first detection power based on output of the first variable amplifier and second detection power based on output of the second variable power amplifier, the variable power amplification control means controls the first and second variable power amplifiers in response to a transmission power control bit sent from a station to communicate with and the difference between the first detection power and the second detection power, and the switch control means switches the operation of the first variable power amplifier and the operation of the second variable power amplifier in response to the detection power difference.
Furthermore, the variable power amplification control means controls the first and second variable power amplifiers so that the detection power difference approaches zero, and the switch control means turns off the first variable power amplifier when the detection power difference is almost eliminated.
Moreover, the radio communication device further includes analog-digital batch conversion means having a first multiplier for multiplying the first detection power and the second detection power by random code having orthogonality, an adder for adding output of the first multiplier, an analog-digital converter for converting output of the adder into digital signal, and a second multiplier for multiplying output of the analog-digital converter by the random code as means for converting the first detection power and the second detection power output from the transmission power detection means into digital signals in batch.
According to the invention, there is provided a transmission power control method in a radio communication device for controlling power transmitted to a station to communicate with, the transmission power control method comprising a variable power amplification control step of controlling a variable power amplification means including at least first and second variable power amplifiers, each capable of varying its amplification gain, a transmission power detection step of detecting transmission power of the radio communication device based on output of the variable power amplification means, and a switch control step of performing switch control for the operation of the variable power amplification means in response to the detected transmission power.
Further, the transmission power detection step detects first detection power based on output of the first variable power amplifier and second detection power based on output of the second variable power amplifier, the variable power amplification control step controls the first and second variable power amplifiers in response to a transmission power control bit sent from a station to communicate with and the difference between the first detection power and the second detection power, and the switch control step switches the operation of the first variable power amplifier and the operation of the second variable power amplifier in response to the detection power difference.
Furthermore, the variable power amplification control step controls the first and second variable power amplifiers so that the detection power difference approaches zero, and the switch control step turns off the first variable power amplifier when the detection power difference is almost eliminated.
Moreover, the transmission power control method further comprises the analog-digital batch conversion steps containing a first multiplication step of multiplying the first detection power and the second detection power by random code having orthogonality, an addition step of adding output of the first multiplication step, an analog-digital conversion step of converting output of the addition step into digital signal, and a second multiplication step of multiplying output of the analog-digital conversion step by the random code as steps of converting the first detection power and the second detection power output from the transmission power detection step into digital signals in batch.
In the radio communication device and the transmission power control method of the invention, switch control is performed for the operation of the variable power amplification means containing the first and second variable power amplifier in response to the detected transmission power, and power transmitted to the station to communicate with. At this time, the variable power amplification means are switched for operation in response to the detected transmission power, so that a wide range of transmission power control can be performed with high accuracy in the simple configuration; the operation of variable power amplification means can be turned off for lower power consumption and the unit can be miniaturized.
Further, in the radio communication device and the transmission power control method, the first detection power based on output of the first variable power amplifier and the second detection power based on output of the second variable power amplifier are detected, the first and second variable power amplifiers are controlled in response to the difference between the first detection power and the second detection power and the transmission power control bit sent from the station to communicate with, and the operation of the first power amplifier and the operation of the second variable power amplifier are switched in response to the detection power difference. Thus, it is made possible to reduce power consumption by turning off the operation of variable power amplification means while the accuracy of the transmission power control is maintained.
Furthermore, in the radio communication device and the transmission power control method, the first and second variable power amplifiers are controlled so that the detection power difference approaches zero, and the first power amplifier is turned off when the detection power difference is almost eliminated, whereby the time period over which power supply to the variable power amplification means is stopped can be prolonged, thus the number of circuits that can be powered off can be increased, and power consumption can be decreased.
Moreover, in the radio communication device and the transmission power control method, the first detection power and the second detection power are multiplied by random code having orthogonality, the results are added, and the resultant signal is converted from analog form into digital form, then the digital signal is multiplied by the above-mentioned random code, whereby the digital signal is separated corresponding to the former analog signals, namely, the first detection power and the second detection power can be converted into digital signals in batch. Thus, the number of the circuits of the analog-digital converter, etc., can be reduced and the unit can be miniaturized.